Microscale interpretation of tribological phenomena in Ti/TiN soft-hard multilayer coatings on soft austenite steel substrates

Abstract

Abstract. The mechanical and tribological behavior of physical vapor deposited coatings on soft substrate materials gains increasing interest due to economical and environmental aspects -e.g. substitution of steels by light-weight metals or polymers in transport vehicles. Nevertheless, such soft materials require surface protection against wear in tribological contacts. Single layer hard coatings deposited at room temperature are brittle with a relatively poor adhesion. Therefore, they should be better substituted by tough multilayer coatings of soft-hard material combinations. However, the mechanics of such multilayer coatings with several 10 nm thick bilayer periods is difficult and yet not well described. The presented work tries to fill the gap of knowledge by focusing both on mechanical investigations of hardness, adhesion, and wear and on microscopic elucidation of deformation mechanisms. In the paper 1 µm thick Ti/TiN multilayer stacks were deposited by magnetron sputtering on soft austenitic steel substrates at room temperature to prevent distortion of functional components in future applications. High hardness was found for 8 and 16 bilayer films with modulation ratio Ti:TiN = 1:2 and 1:4. This was attributed (with use of transmission electron microscopy) to stopping the crack propagation in thin Ti layers of the multilayer systems by shear deformation combined with different fracture mechanisms in comparison with that for the TiN single layers (edge cracks at the border of the contact area and ring cracks outside, respectively).

Deformation, failure and removal mechanisms of thin film structures in abrasive machining

“…A reduction of about 35% in maximum shear stress was achieved. Given that the lateral cracking was governed by shear stresses, the study clearly demonstrated that the use of a multilayer structure could significantly increase the shear strength of a structure [53,54].…”

Tribology and Micromechanics of Chromium Nitride Based Multilayer Coatings on Soft and Hard Substrates

“…Unbalanced magnetron sputtering in an industrially-scaled, 4 rectangular cathode vacuum chamber was chosen to deposit Cr, CrN, and DLC coatings from high purity chromium (99.99%, RHP Technology GmbH, Seibersdorf, Austria) and electrographite carbon targets (99.9%, Schunk Group, Bad Goisern, Austria), respectively. The following coating architectures were developed based on former works [19,20]:…”

Roughness Influence On Macro- And Micro-Tribology Of Multi-Layered Hard Coatings On Carbon Fibre Polymer Composite

“…As a result, the coating shows no total failure, but only the formation of deformation bands, which are tilted towards the substrate depending on the hard-soft phase thickness ratio [9]. We presented such results recently for titanium-titanium nitride, chromium-chromium nitride (Cr-Cr 2 N) and other multilayer systems [8,9]. The micro-scale deformation mechanism within the deformation bands comprises strain hardening and broadening of the deformation under too high loads instead of fracture [9].…”

“…If such a composite is coated, wrinkling of the epoxy matrix leads to high local tensile strains in the coating on the micro scale with risk to fracture [6,7]. Local bending deformation of the soft epoxy matrix occurs under high tribological point loading too, as recently shown in own works for magnetron sputtered coatings [8]. Single-layered coatings fail by cohesive cracking through the whole thickness with a crack start at the surface or the interface depending on the type of bending.…”